1. Field of the Invention
This invention relates to a fuel pump control system for cylinder cut-off internal combustion engine.
2. Description of the Related Art
In one prior art method, the fuel pump for supplying pressurized fuel to the fuel injectors of an internal combustion engine is driven under a constant applied voltage (constant delivery flow rate) while recirculating excess fuel beyond the fuel amount (quantity) required by the engine to the fuel tank through a regulator installed in a pipe inside the fuel tank. The implementation of the excess fuel recirculation system in the fuel tank in this manner simplifies the piping structure and also helps to prevent temperature increase of the fuel in the fuel tank.
When a fuel pump is driven at a constant applied voltage in the foregoing manner, the applied voltage has to be set at a high value (the delivery flow rate has to be made large) so that the supply of fuel does not become deficient even when the fuel amount required by the engine is maximum. When the required fuel amount is small, therefore, much of the fuel pressurized by the fuel pump comes to be recirculated to the fuel tank as excess fuel. This lowers efficiency. Specifically, when the fuel amount required by the engine is small, the fuel pump is supplied with an amount of electric power greater than that needed to supply the required fuel amount, so that the fuel pump consumes a larger than necessary amount of power. Moreover, the operating noise of the fuel pump is maintained at a higher level than necessary.
This led to the idea taught by Japanese Laid-Open Patent Application No. Hei 11(1999)-182371 of calculating a value proportional to the fuel consumption based on the engine speed and then switching the delivery flow rate of the fuel pump between two levels (high flow rate and low flow rate) based on the calculated value.
However, it has also been proposed to improve fuel consumption by switching engine operation, based on the engine load, between full-cylinder operation during which all of the cylinders are supplied with fuel to be operative and cut-off-cylinder operation during which the fuel supply to some of the cylinders are cut-off or stopped to be non-operative, as disclosed in Japanese Laid-Open Patent Application No. Hei 10(1998)-103097.